1. Field of the Invention
The present disclosure relates to a liquid drop ejecting head which ejects liquid drops from nozzles, an image forming device including the liquid drop ejecting head to form an image on a print medium by ejecting liquid drops, and a method of manufacturing the liquid drop ejecting head.
2. Description of the Related Art
A liquid drop ejecting head which ejects liquid drops from nozzles is used, for example, as a printing head in image forming devices, such as copiers, printers, facsimile devices, plotters, and multi-function peripherals. The image forming device is a device which forms an image on a print medium by ejecting liquid drops to the print medium. In the following, the material of the print medium is not limited to paper, and the print medium used in the image forming devices of the liquid drop ejection type may include all printing sheets (paper), yarn, fibers, textile, leather, metal, plastics, glass, wood, and ceramics. The image formation performed by the image forming devices of the liquid drop ejection type may include image formation of meaningful images, such as characters or figures, and image formation of meaningless images, such as patterns, (in which liquid drop ejection is formed). The liquid used in the image forming devices of the liquid drop ejection type is not limited to ink and may include printing liquid (ink), fixing process solutions, DNA samples, resist materials, pattern materials, resins, etc.
Conventionally, there is known a liquid drop ejecting head which is commonly used in the image forming devices described above. This liquid drop ejecting head generally includes a nozzle plate, a channel plate, a diaphragm, and a pressure generating unit. The nozzle plate forms one or plural nozzles provided therein. The channel plate is a plate member which forms a common liquid chamber and individual liquid chambers. The individual liquid chambers are provided corresponding to the nozzles respectively and communicate with the nozzles. The common liquid chamber communicates with the individual liquid chambers and supplies liquid to the individual liquid chambers. The diaphragm is a component which forms a part of the individual liquid chambers and transmits pressure oscillation given by deformations of the pressure generating unit to the liquid in the individual liquid chambers. The diaphragm is deformed by the pressure generating unit in accordance with a liquid drop eject signal received from the host device, and the pressure oscillation from the pressure generating unit is transmitted to the liquid in the individual liquid chambers through the diaphragm. For example, a piezoelectric actuator is used as the pressure generating unit.
In this liquid drop ejecting head, the pressure oscillation by the pressure generating unit is given to the diaphragm in accordance with the liquid drop eject signal from the host device. The deformations of the diaphragm due to the pressure oscillation are transmitted to the liquid in the individual liquid chambers to exert pressure on the liquid and eject liquid drops from the nozzles of the nozzle plate to a print medium.
In recent years, various kinds of ink are used in an ink jet printing head which is a typical example of the liquid drop ejecting head. Especially, when an alkaline ink is used and a liquid chamber substrate to form an ink jet printing head is made of a silicon material, there is a problem that inner side walls of a liquid chamber formed in the liquid chamber substrate are easily eroded by the alkaline ink.
Japanese Laid-Open Patent Publication No. 2008-105334 discloses a liquid drop ejecting head in which a protection film is formed to cover the inner side walls of the liquid chamber, in order to prevent the corrosion of the inner side walls by alkaline inks. In a case of the liquid drop ejecting head of Japanese Laid-Open Patent Publication No. 2008-105334, a liquid chamber is formed in a liquid chamber substrate by etching, and by using a plasma polymerization method, a film of an oxide of silicon dioxide is deposited as a protection film on the inner side walls of the liquid chamber that may contact an alkaline liquid material. By using the plasma polymerized film, good liquid resistance to the alkaline liquid is obtained. In the following, a film which is formed by using the plasma polymerization method is called plasma polymerized film.
However, in the liquid drop ejecting head of Japanese Laid-Open Patent Publication No. 2008-105334, after etching of the liquid chamber substrate to form the liquid chamber is performed, the plasma polymerized film is formed on the inner side walls of the liquid chamber using the plasma polymerization method. It has been difficult to form a uniform plasma polymerized film having a predetermined thickness on the inner side walls of the liquid chamber.
Specifically, the plasma polymerization method is a film deposition method in which a plasma polymerized film is formed by causing the ionized components of the plasma polymerized film between the mutually opposed electrodes to adhere to the film deposition object disposed between the electrodes. For this reason, in the liquid chamber formed by etching the liquid chamber substrate, the plasma polymerized film is uniformly formed on the surfaces facing the electrodes, but the ionized components of the plasma polymerized film cannot easily be caused to adhere to the surfaces parallel to the surfaces facing the electrodes. As a result, the thickness distribution of the plasma polymerized film formed is not uniform, and a thin portion in the thickness distribution which is less than a predetermined thickness is vulnerable to erosion. The liquid resistance of such a thin portion becomes excessively low.
In addition to the above-described plasma polymerization method, a thermal oxidation method is known as a film deposition method for forming an oxide film of silicon dioxide. In this thermal oxidation method, an oxide film is deposited at high temperature, and there has been a problem that the liquid chamber substrate which forms the liquid chamber is deformed by the heating.